80 PROFESSOR T. MCKENNY HUGHES, M.A. 
upon the coast, and explain how caves must everywhere 
be formed where shattered or softer rock is exposed to the 
lash of the wind-driven sea. 
But this is not all. The wave picks up great boulders and 
hurlsthem at the rocks that bar its advance. Itis quite common, 
after a storm, to find large stones lodged on a promenade or 
pier, where they must have been caught up zm the wave and 
thrown upon the land. Stones are always carried forward up 
an incline as far as the waves advance; but the cases I refer 
to now are those in which the stone has been thrown up to 
the top of a vertical wall. The last place I remember having 
seen this was in a great storm a few years ago at Hunstanton. 
The same thing takes place on a grand scale on some of the 
wild, rocky cliffs of North-Western Scotland, for instance. 
The Director-General of the Survey has described how in 
storm, great blocks are hurled up on to the top of the chff 
near the Old Man of Hoy. 
The force of the Atlantic waves at the Skerryvore Rocks, 
as estimated by the marine dynamometer, an instrument 
designed by Thos. Stevenson for this purpose, was found to 
be as much as 6,083 lb. to the square foot.* 
From the height to which the spray was thrown, he inferred 
a pressure of about 3 tons to the square foot; and further 
recorded that a block of stone, estimated at 48 tons in weight, 
*‘ was seen to move under the influence of each wave.” + 
“On the Bound Skerry of Whalsey, which is only exposed to the waves 
of the North Sea or German Ocean, he had found .... masses of rock 
weighing 93 tons and under, heaped together by the action of the waves at 
the level of no less than 62 feet above the sea ; and others ranging from 6 
to 135 tons were found to have been quarried out of their positions a situ, 
at levels of from 70 to 74 feet above the sea. Another block of 74% tons, at 
the level of 20 feet above the sea, had been quarried out and transported to 
a distance of 73 feet . . . . over opposing abrupt faces as much as 7 feet in 
height.” t 
It is clear that such waves and such boulders would make 
short work of broken rock or a rotten dyke, and any old 
cave or fissure opened out by the sea would not be likely to 
have much of the original deposits left in it. The first storm 
would clear ont all earth and bones, and leave in its place 
only the well-worn pebbles of a rocky shore,—the battered 
shot of nature’s great marine artillery. A sudden upheaval 
would leave the cave either quite clear, if it was on a clean, 
\ 
* Stevenson, Thos. Hdin. New Phil. Jour. xlviii. 1850, p. 41. 
+ Ditto, Proc. RK. Soc. Edin. vol. ii. 1844-50, p. 13. 
{t Ditto, Proc. R. Soc. Edin. vol. iv. 1862, p. 200. 
